The deeper truth you are talking about is spiritual understanding , which only comes from the Holy Spirit. They couldn't understand, so he had to talk about nothing but Jesus and him Crucified. 1 Cor:2:6 -8 6 We do, however, speak a message of wisdom among the mature, but not the wisdom of this age or of the rulers of this age, who are coming to nothing. 7 No, we declare God’s wisdom, a mystery that has been hidden and that God destined for our glory before time began. 8 None of the rulers of this age understood it, for if they had, they would not have crucified the Lord of glory
This is talking about the deeper truth ," as you put it". It's for the mature.